A turbomachine, for example a gas turbine, has a casing which for reasons of assemblability of the gas turbine is constructed in a horizontally and/or vertically split manner. The split turbomachine casing for example has a top section and a bottom section which are assembled together, forming a parting joint.
In FIG. 8, the region of the parting joint of a known turbomachine casing 101 is shown in cross section. The turbomachine casing 101 has a top section 102 and a bottom section 103, which together form a parting joint 104. During operation of the turbomachine, the turbomachine casing 101 as a rule is under pressure so that on the inner side 105 of the turbomachine casing 101 a higher gas pressure prevails compared with the outer side 106.
At the parting joint 104, an upper flange 107 is formed on the top section 102, and similarly at the parting joint 104 a lower flange 108 is formed on the bottom section 103, wherein the two flanges 107, 108 form the parting joint 104 by their sides which face each other. Both through the upper flange 107 and through the lower flange 108 provision is made for a flange hole 109 through which a parting-joint stud bolt 110 is inserted. The parting joint stud bolt 110 projects from the upper flange 107 and from the lower flange 108 in each case, wherein the parting joint stud bolt 110 has a threaded portion 111 on its outer sections in each case. Between the threaded portions 111, the parting joint stud bolt 110 is provided with a waisted shank 112. A threaded nut 113, with a washer 114, is screwed on the threaded portions 111 in each case so that by the threaded connection which is thereby created the upper flange 107 and the lower flange 108 are pressed against each other. The force flux which occurs in the top section 102, in the bottom section 103, in the parting joint stud bolt 110, in the threaded nuts 113 and in the washers 114, is shown schematically by arrows 115.
As a result of the threaded connection which is created by the parting-joint stud bolts 110 on the upper flange 107 and on the lower flange 108, the two flanges 107, 108 are fastened to each other in a frictionally engaging manner in the horizontal direction 116.
It is desirable for the parting joint 104 to be as gas leakage-free as possible so that leakage which occurs through the parting joint 104 from the inner side 105 to the outer side 106 during operation of the turbomachine gas is as small as possible.
The reason for the gas leakage is especially the time-delayed and uneven heating-through of the flanges 107, 108 together with the parting joint stud bolt 110, with the threaded nuts 113 and the washers 114 during the non-steady state operation of the turbomachine. The parting joint stud bolt 110 in particular is effected by the delayed heating-up since for construction-related reasons it is generally positioned a long way from the place of heat entry and can only be heated up via small contact surface areas on the threaded portions 111.
Particularly in the casing region which on the inner side is exposed to compressor exit conditions, extremely large temperature differences occur between the upper flange 107 or the lower flange 108 and the waisted shank 112 during cold starting. These temperature differences lead to correspondingly large differences in the thermal expansion of the components in question. As a result of this, a single over-elongation of the parting-joint stud bolt 110 occurs during the very first start-up of the turbomachine, which results in a permanent reduction of the pretension of the parting-joint stud bolt 110 and therefore in a reduction of the surface area pressure at the parting joint 104. In addition, the upper flange 107 and the lower flange 108 deform in relation to each other on account of their inhomogenous heating-through, which in combination with the reduced pretension of the parting-joint stud bolt 110 leads to a gap at the parting joint 104. As a result, a gas leakage occurs at the parting joint 104.
The gas leakage is particularly large in the region of the turbomachine casing 101 at which a plurality of parting joints 104 intersect. In the region of intersection, on account of the provision of upper flanges 107 and lower flanges 108 for each parting joint 104, the wall thickness of the turbomachine casing 101 is particularly large so that during start-up of the turbomachine large temperature differences can occur in its material in the region of intersection. It should be added that owing to the geometrically confined conditions optimum threaded-joint tightness of the parting-joint stud bolts 110 cannot be provided on account of collisions of threaded-joints. Therefore, the region of intersection is characterized by particularly high rates of gas leakage.
The development of modern gas turbines is particularly to the effect that the compression ratio is to be increased significantly by 1.5 to 2 compared with today's customary factors. The even higher flange forces which result from this, and also the even higher compressor exit temperatures, would have the result that higher gas leakage rates would need to be reckoned with in modern turbomachine casings with the conventional construction at the parting joint 104 with the upper flange 107, the lower flange 108 and the parting-joint stud bolt 110. Moreover, the upper flange 107 and the lower flange 108 would have to be dimensioned larger and would have to be produced from a higher-grade material in order to cope with the anticipated higher compressor exit temperature and the increased pressure. Both measures lead to a cost increase and to a deterioration of the boundary conditions for the conventional flange construction since an even longer heat transporting path and an even more uneven heating-up resulting therefrom together would be associated with even greater loss of pretension of the parting-joint stud bolt.
In addition, in the region of the parting joint 104 the turbomachine casing 101 has the force flux 115 which is asymmetrical. Consequently, during cold starting the parting-joint stud bolt 110, in addition to pure tensile forces, also experiences a bending stress, which intensifies the uneven thermal expansion in the region of the parting joint 104. In order to take into account the bending stress of the parting joint stud bolt 110, a correspondingly stable design of the threaded joint and a correspondingly thick construction of the upper flange 107 and of the lower flange 108 are to be provided. This, however, would result in a further deterioration of the uneven temperature distribution in the region of the parting joint.
Furthermore, a casing for a turbomachine with two abutting casing shells is known for example from EP 1 707 759 A2. In order to avoid asymmetrical deformation of the casing during operation of the machine, a form-fitting connection by means of a bridge, which clamps the two shells together, is provided on the outer side of the casing.
Furthermore, a connection of casing sections of a high-pressure vessel is disclosed in laid-out specification DE 1 160 701, which in addition to a customary external bolted flange joint has a clamping arrangement with wedge taper on the inner side of the casing.